A gas turbine engine includes one or more shafts which are mounted for rotation in several bearings, usually of the rolling-element type. The bearings are enclosed in enclosures called “bearing sumps” which are pressurized and supplied with an oil flow for lubrication and cooling. In most cases one of the boundaries of the bearing sump will be a dynamic seal between a rotating component of the engine and an engine stationary structure. Various tubes, collectively referred to herein as “service tubes”, are used to supply oil to the bearing sump (an “oil supply tube”), to drain spent oil from the bearing sump (a “drain” or “scavenge tube”), to pressurize the bearing sump with air (a “pressure tube”), and to vent air from the bearing sump (a “ventilation tube”).
The bearings and bearing sumps are mounted within a casing of the engine using a stationary structural frame that provides a structural load path from the bearings. An exemplary conventional stationary structural frame may include a central hub connected to an annular outer rim with a plurality of radial struts. The service tubes are frequently routed internally of the struts, sometimes in a limited frame strut area, that challenges the ability to route the service tubes (oil supply, scavenge, pressure, and ventilation tubes) to bearing sumps. In addition, a conventional stationary structural frame may cross the flowpath of the turbine, thus exposing the service tubes to high temperatures in operation. After the engine stops, the oil that normally cools the bearings stops flowing. The heat stored in the turbine then raises the temperature of the bearings much higher than when the engine was running, tending to cause undesirable oil coking within the service tubes. “Coking” refers to the undesirable accumulation of carbon particles. Increased coking may lead to increased seal wear and adversely impacts bearing life. Increased oil coking can also result in removal of the engine from service and can increase engine overhaul costs.
Accordingly, it is desirable to provide thermal isolating service tubes and assemblies thereof for gas turbine engines that are configured to provide thermal isolation from high external temperatures (e.g., from hot combustion gas) to reduce heat loads and coking therein, resulting in reduced maintenance, reduced heat rejection requirements, increased bearing and engine life, reduced overhaul requirements, and reduced engine removals. It is also desirable to provide thermal isolating service tubes and assemblies thereof for gas turbine engines that enable easier routing of the tubes within the gas turbine engine. Furthermore, other desirable features and characteristics of the present invention according to exemplary embodiments will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the preceding background.